The question is based on the thread.
How can you allow only one user to access the display by xhost?
sudo xhost masi is not working in my fresh Ubuntu 9.10.
I'm testing on Ubuntu 12.04 with X.Org X Server 1.11.3.
I tried Johan's solution and it appeared at first to work, but I found on my system the text after "local:" was being ignored. The result was that all local users were given access to my X session rather than one user.
The magic I found worked was:
Replace the portion after the last colon with the username you wish to grant access. You can inspect the authorised list by running xhost with no paramters. It should look something like:
This indicates that the "masi" user and the "myself" user are being granted xhost permissions in the same way.
First, restrict X server access to those who aren't on the list:
sudo xhost -
then add yourself to the allow list:
sudo xhost +masi
Basically the same as John T, but you could add inet or local to the command